Drilling into the earth, for example, to recover hydrocarbons is typically done with a drill rig. The drill rig is located at a well center from which a wellbore is extended into the earth using a rotating drill bit at the downhole end of a drill string. The drill string is made up of tubular sections that are coupled together. These sections are typically called ‘tubulars’ or ‘pipe’ or ‘joints’.
During drilling, drilling fluid, often called ‘mud’ is pumped through a bore of the drill string. The drilling fluid exits at the drill bit and returns to the surface carrying cuttings from the drilling operation in an annulus surrounding the drill string. In addition to carrying the cuttings the drilling fluid may assist in keeping the wellbore open against subsurface pressures.
As the wellbore is extended, more tubulars are added at the uphole end of the drill string. The tubulars are most typically coupled together by threaded couplings. The thread dimensions and geometry can vary but are usually selected to be one of a number of standard threads specified by the American Petroleum Institute (API) in API specification 7-2 (ISO 10424).
In drilling it is sometimes necessary to remove the drill string from the wellbore or to introduce a drill string into a wellbore that has already been partially completed. This is called ‘tripping’. Tripping may be done, for example, to replace a worn drill bit. Tripping can be done much more quickly than drilling.
Most drill rigs have floors that are elevated. The patent literature describes various pipe handling systems that can present an end of a tubular at the rig floor from where the tubular can be hoisted by equipment on the drill rig or that can carry a tubular away from the rig floor. These include the following patent publications: US 2004/0136813; US 2005/0079044; US 2005/0238463; US 2006/0124356; US 2009/0053013; US 2006/0104746; US 2006/0285941; U.S. Pat. Nos. 7,404,697; 7,163,367; 7,021,880; 6,994,505; 6,533,519; 6,079,925; 5,122,023; 4,403,898; 4,386,883; 4,382,738; 4,379,676; 4,347,028; 4,494,899; 4,235,566; 4,067,453; 3,655,071; 3,053,401; CA 2510137; WO 99/29999; US 2013/0341096; WO 2005/059299; WO 2013/191733; WO 2013/173459; WO 2013/169700; WO 2011/017471; WO 2009/026205; WO 2006/059910; WO 2009/055590; US 2015/0184472; US 2015/0139773; US 2015/0008038; US 2014/0126979; US 2012/0039688; US 2011/0200412; US 2011/0044787; US 2011/0030942; US 2010/0254784; US 2010/0135750; US 2009/0136326; US 2012/0130537; US 2012/0118639; US 2004/0197166; US 2003/0159854; US 2003/0123955; US 2007/0221385; U.S. Pat. Nos. 8,469,085; 8,215,887; 8,210,279; 8,186,455; 8,052,368; 7,992,646; 7,967,540; 8,764,368; 8,632,111; 8,584,773; 8,079,796; 7,802,636; 7,762,343; 7,431,550; 6,997,265; 7,918,636; 7,832,974; 6,705,414; 6,695,559; 6,609,573; 6,220,807; 5,451,129; 5,107,940; 6,976,540; 6,719,515; 4,439,091; 4,426,182; 4,365,692; 4,453,872; GB 2462390; GB 2442430; 4,040,524; 3,865,256; 3,065,865; 2,958,430; GB 8513524; GB 2152113; GB 2152112; GB 2152111; GB 2125862; GB 2085047; GB 2351985; GB 2162485; GB 2158131; GB 2152561; GB 2152115; GB1303618; EP 1038088; EP 0061473; EP 2425090; and, EP 1723306.
Many of the prior art systems present the ends of tubulars near the edge of the drill rig floor. When the tubulars are hoisted by the drill rig, the tubulars can pendulum after their trailing ends are lifted free. Drill rig personnel often have the task of steadying the tubulars. This is physically challenging. Tubulars are heavy. Small 2⅜ inch diameter tubulars typically weight about 7 pounds per foot (about 10 kg/m). Larger 5 inch diameter tubulars typically weigh about 25 pounds per foot (about 37 kg/m). Larger drill collars can weigh 300 pounds per foot (about 443 kg/m) or more. This work is also potentially dangerous. Personnel are forced to work near the well center. The floor can be slippery as a result of spilled drilling mud. Drilling is sometimes performed in poor weather which increases the risk to drill rig personnel.
Drill rigs are extremely expensive to operate. It is therefore important to be able to quickly bring in additional tubulars to extend a drill string or to remove tubulars from the well center, especially while tripping.
Tubulars can have various lengths. A typical length is approximately 30 feet (about 10 meters). ‘Range II’ tubulars have lengths of about 31 feet. ‘Range III’ tubulars have lengths of about 46 feet. Each range has a tolerance. For example, Range III tubulars should have a minimum length of 42 feet and a maximum length of 48 feet. Equipment for handling tubulars in a particular length range ought to accommodate tubulars having any length between the minimum and maximum lengths specified for the range. Many drill rigs can accommodate sections of drill string up to about 90 feet long. Sometimes a number of tubulars may be coupled together in advance to yield a ‘stand’. For example, three Range II tubulars may be coupled together to yield a ‘triple’. As another example, two Range III tubulars may be coupled together to make a stand. Handling stands instead of individual tubulars can make the drilling operation (especially tripping) faster. However, stands are generally too long to conveniently transport on land.
There is a need for safe and efficient apparatus and methods for delivering tubulars to or from a drill rig. There is also a need for safe and efficient apparatus for building and unbuilding stands of tubulars.